THERMAL-EXPANSION PROPERTIES OF METALLIC AND CERMET COATINGS

Free-standing deposits of NiCrAl, stainless steel, and 8 wt.% yttria-s tabilized zirconia were prepared using atmospheric plasma spraying and high velocity oxygen fuel processing. Feedstock powders were blended, yielding mixtures (by weight) of 100%, 75%, and 50% of the metallic m aterial. Porosity and composition (i.e. metal or ceramic constituents) of these deposits were measured by image analysis. The coefficient of thermal expansion (CTE) was measured in the 200-950 degrees C interva l for four thermal cycles. The first runs of these CTE measurements we re not linear and differentiation of this curve established the CTE de pendence with respect to temperature. Maximums in CTE behavior suggest that stress relaxation and/or oxidation may be occurring. Measurement s of CTE from thermal cycles after the first cycle were constant and o beyed the law of mixtures in the measured temperature region, suggesti ng that stress relaxation and/or oxidation, evident in the first cycle , are no longer dominant. Microstructural analysis and microhardness m easurements were used to confirm the findings from CTE measurements. ( C) 1998 Elsevier Science S.A.